A Study of Desiccation in the Rotifer, Philodina Roseola, With Special Reference to Cytological Changes Accompanying Desiccation

The tissues and the parts of the individual cells of a desiccated Philodina roseola maintain their identity during the drying process. 2. No protecting membrane is secreted when drying begins or at any other time during the desiccation process. The integument of the dried rotifer is thinner than that of the undried specimen. 3. Metabolism goes on slowly in the dry condition as is evidenced by changes in the walls of the digestive tube. 4. Desiccation in Philodina may be complete but not absolute without fatal results. 5. The typical nucleus in all the tissues of Philodina consists of a single large karyosome surrounded by a clear space with a distinct nuclear membrane at the periphery of the clear space. 6. The general effect of desiccation upon the cells of the rotifer tissues is the production of a nuclear-cytoplasmic rearrangement in which the chromatic part of the nucleus migrates to the periphery and the cytoplasm becomes more dense. 7. The movement of chromatin during desiccation phenomena takes place in order that the cell oxidations may continue during the dried condition. 8. The extent of the structural rearrangement which takes place in the rotifer cells is not directly proportional to the intensity of the stimulus. 9. In animals recovering from desiccation the elements of nucleus and cytoplasm gradually resume normal relationships. 10. The chromatic rearrangement in the nuclei of cells of drying rotifers takes place at the very beginning of the drying process. 11. The acceleration of reproductive activity just subsequent to drying is traceable to an increase in ovarian nuclei. This increase takes place while the animal is recovering. 12. The cytological changes attending a recovery from desiccation are in their nature the exact reverse of those taking place during the drying process. 13. The death of cells as a result of desiccation is probably not a result of the activity of concentrated osmotic materials upon the protoplasm as Pfeffer suggests. 14. The death of rotifers during the desiccation process may be due to one or a combination of the following causes: (1) Mechanical injury due to too rapid drying, (2) starvation resulting from a lack of reserve food material, (3) the poisonous effect of metabolic products and (4) insufficient time before drying to effect the nuclear-cytoplasmic reorganization.